The invention is in the field of hot bar soldering of the leads of surface mountable components (so-called SMC's) to conductive tracks on the surface of circuit boards or the like and, more particularly, is directed to a floating suspension of the hot bars or thermodes.
Each site on a circuit board at which an SMC is to be mounted has conductive solder pads arranged thereon in a pattern which is identical to a pattern defined by the tips of the leads of the component.
The above-referenced U.S. patent application Ser. No. 463,456 is illustrative of a device for attaching the leads to the solder pads by applying heat and pressure. Each component is held by vacuum to the tip of a hollow spindle so that it may be transported and placed on the circuit board by the spindle, with each component lead resting on a corresponding solder pad. Then, a coaxially supported arrangement of heating bars is telescoped down into engagement with the leads, such that each bar contacts all of the leads which are situated along a corresponding edge of the component. Typically, the bars are applied to the leads with heat enough to melt the solder and with pressure sufficient to push the leads through the melted solder and into contact with conductive tracks of the circuit board, after which the heating is halted sufficiently for the solder to resolidify.
A typical problem with hot-bar soldering has been maintaining contact between the thermodes and the component leads during the soldering cycle. If the plane formed by the working surface of the thermodes is not parallel to the plane defined by the traces of the substrate, uneven heating of the solder will occur.
The above-referenced U.S. Pat. No. 4,768,702 provides for "floating" of the thermodes of a hot-bar soldering device, wherein the thermode assembly is suspended by means of a pair of quadrilateral linkage mechanisms situated at right angles to each other. Thus, a thermode working surface is tiltable to conform to a work surface inclination during advancement of the thermode into engagement with the work.
It is an object of the invention to utilize a quadrilateral linkage floating support for a thermode in such a way as to overcome problems that would be encountered by the device of U.S. Pat. No. 4,768,702 in attempting to hot-bar solder the leads of components on the order of size of so-called "square packs" which are about 1-2 inches on a side.
It is also an object of the invention to overcome problems encountered when hot-bar soldering such components with thermodes which are tiltable by means other than a quadrilateral linkage arrangement.
More specifically, it is an object of the invention to prevent shifting of the work along the substrate by the thermode working surface which is at an angle to the work surface plane during initial contact and prior to achieving a smooth interface therebetween.
Further, it is an object of the invention to improve the solder bonds resulting from hot-bar soldering while also minimizing subsequent bonding failures which can occur when a lead deviates from a nominal work surface plane prior to being contacted by the thermode.
These and other objects of the invention will become more apparent from the following disclosure.